Research into the injuries inflicted by the police on arrested people in Illinois:

http://www.sciencedaily.com/releases/2016/01/160129090504.htm

The conclusion is: you're less likely to get seriously hurt in a confrontation with a random drunken thug in a bar than if you have to deal with a stone cold sober trained police officer on duty. The cops are also much more likely to injure the mentally ill or partly paralyzed than the thugs are, you are much more likely to get kicked in the back when lying on the ground unable to defend yourself, and as measured by length of hospital stay, you will probably be twice as badly hurt. Oh, and there's a 90% chance that after you get out of hospital, you won't be convicted of anything meriting imprisonment.